Substrates in power electronics usually provide interconnections for forming an electric circuit (e.g. a printed circuit board), as well as, for heat dissipation from the components. In comparison to materials and technologies used for lower power microelectronics, power electronic substrates should provide higher current capacity and higher voltage isolation which might be voltages up to several thousand volts. Furthermore, these power electronic substrates also should operate over a wide temperature range, such as up to about 150° C. or even 200° C.
One substrate of the conventionally used substrates is the direct bonded copper (DBC) substrate which is commonly used in power electronic modules due to their high thermal conductivity. The DBCs are usually composed of a ceramic tile conventionally manufactured of a metal oxide or nitride (e.g. aluminum oxide, aluminum nitride, and the like) with at least one layer (e.g. with at least one metal sheet or metal foil) of copper bonded to one or both sides of the ceramic tile by means of a high-temperature oxidation process, wherein the one or more copper layers and substrate are heated to a controlled temperature in an nitrogen atmosphere. Under these conditions, a copper-oxygen eutectic is formed which bonds to the one or more copper layers and the oxides used as a substrate such that a common substrate is formed. The top copper layer can be prefabricated, such as by means of a heat treatment, an ablation process and/or etching using a conventional printed circuit board technology to form an electrical circuit, while the bottom copper layer is usually kept plain. Conventionally, the substrate is attached to a heat spreader by means of soldering the bottom copper layer to the substrate. Moreover, conventional ceramic material used in DBC substrates include typically metal oxides or nitrides, such as alumina (aluminum oxide, Al2O3), which is widely used because of its low cost, but alumina has however low thermal conductivity (about 24 W/mK to about 28 W/mK) and is highly brittle; aluminum nitride (AlN), which is more expensive, but has a better thermal performance (about 150 W/mK to about 230 W/mK); and beryllium oxide (BeO), which has an improved thermal performance (about 330 W/mK), but is often avoided, because of its high toxicity when the powder is ingested or inhaled. One characteristic of the DBC substrates is their low coefficient of thermal expansion, which is close to that of silicon (compared to pure copper). This characteristic ensures good thermal cycling performances (up to about 50,000 cycles). The DBC substrates also have excellent electrical insulation and good heat spreading characteristics. A related technique uses a seed layer, photoimaging, and then additional copper plating to allow for fine lines (as small as 50 μm) and through-vias to connect front and back sides. This can be combined with polymer-based circuits to create high density substrates that eliminate the requirement for direct connection of power devices to heat sinks.
Currently, there are substantially two approaches for providing heat dissipation by the power electronic substrates. On the one hand, the module is mounted to an external radiator by a thermal heat sink paste, wherein this arrangement has a low thermal conductivity, and on the other hand the module is built up on a so called PinFin plate (i.e. the structure on such a plate is a combination of a pin structure and fin structure formed on one side of the plate) which can be water cooled, such as by means of soldering of the DBC onto this plate, wherein the high material costs for this kind of plates and the still low heat transfer due to the intermediate layer of solder and the thickness of the PinFin plate may be disadvantageous. Moreover, such plates usually allow solely heat dissipation in one direction from the power module, such as the top side or the bottom side of the module.